The Weight-Sensing Hand-controller-less Electric Skateboard

May 28, 2009

V-1 of the weight-sensing electric skateboard.

Here’s the idea:  It’s an electric skateboard with no hand-held controller.  Instead, it senses the portion of the rider’s weight on the fore and aft trucks with strain gauges and commands motor current (~= torque) according to the differential between them.

So the trucks (where the wheels go on) are actually electronic scales.  It knows which way I’m leaning (toward one end of the board or the other), and accelerates in that direction.  That’s pretty much it.

I and the great Frank Schmitt tried to make one of these back in the 20th century when we lived in California.  He’s carrying the torch presently, while I fired all of my guns at once on this proof-of-concept.

I came up with some way to belt-drive the wheels, glued the strain gauges (the little brown rectangular thingies) down to some custom trucks, and hacked together an all-analog (!!!) motor controller that used the strain gauge signals to compute a current command and drive an H-bridge power stage accordingly.

The latter V0 version, upside down to show the complexity

Upside down to show the complexity. The big metal box housed the batteries, and the 9-volts were to deliver +/- 18V to the analog motor controller! (I forget what the black box is.)

Closer-up of the back end.  I think those are Speed-400 motors, one per wheel, belted to pulleys that I somehow screwed onto the wheels.  The strain gauges are visible as little brown rectangles on the trucks.

Closer-up of the back end. I think those are Speed-400 motors, one per wheel, belted to pulleys that I somehow screwed onto the polyurethane wheels. The strain gauges are visible as little brown rectangles on the trucks.

Left of the purple truck piece is the analog-output current sensor, and to the right of it are the current fuses (lot of good they did me).

Left of the purple truck piece is the analog-output current sensor, and to the right are the battery/controller current fuses (lot of good they did me).

(I like how the photography came out.  Thanks to Mom and Dad's 1967 Nikon!)

(I like how the photography came out. Thanks to Mom and Dad's 1967 Nikon!)

My Crap-o-Matic H-bridge power stage for the motors.  (Power electronics is hard.)

My Crap-o-Matic H-bridge power stage for the motors. Notice the SOOT emanating from the second MOSFET! (Power electronics is hard.)

Of course it's an all-analog strain-gauge-informed current-mode DC motor controller.  What else could it be?

Of course it's an all-analog strain-gauge-informed current-mode DC motor controller. What else could it be?

One Saturday night I finally got it all together at work, turned it on, and I swear to God, good people, that it worked for ten seconds.

Ten seconds.

For ten seconds, it responded to my fore/aft shifts in my CG and motored to get under me.

And then the power stage caught fire.

Sadly, that ends my chapter of the story, because I’m just not that into skateboards anymore.  The great Frank Schmitt is making progress a version with just two rolling-pin-style wheels that’ll allow direct-drive motors, which will be very cool.  When he updates me I’ll link to it!  Go go Frankus!

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One Response to “The Weight-Sensing Hand-controller-less Electric Skateboard”

  1. Dan S Says:

    Go go Frankus indeed! I want to see it roll someday. For more than 10 seconds.

    With modern RC power electronics, this project should be a LOT easier. And cheaper. http://www.hobbycity.com is the stuff…


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